Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2002-01-03
2003-12-02
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S209000, C507S211000, C536S020000, C536S055300
Reexamination Certificate
active
06656885
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to the modification of chitosan to produce viscosifiers (thickeners) for aqueous liquids, and to viscosified aqueous fluids containing such modified chitosans dispersed therein, and to methods of drilling a well utilizing such fluids.
BACKGROUND OF THE INVENTION
Many viscosifiers for, and methods of, increasing the viscosity of aqueous liquids are known. Such viscosifiers may be so-called water-soluble polymers such as biopolymers, gums, cellulose derivatives, alginates, and other polysaccharides or polysaccharide derivatives, and various synthetic polymers. Representative polymers are set forth in the book “Handbook of Water Soluble Gums and Resins,” Robert L. Davidson, Ed., 1980.
Viscoelastic fluids are characterized as having a Theological profile which is shear thinning, having a high viscosity at extremely low shear rates and a low viscosity at high shear rates. Thus such fluids are pseudoplastic having a high yield stress.
This type of rheology is produced by hydrating in the fluid certain water soluble polymers or other colloidal materials. These polymers presently known are biopolymers, i.e., microbially produced polysaccharides or heteropolysaccharides, and are well known in the art.
There is a need for fluids which exhibit a high low shear rate viscosity which are shear thinning.
Chitosan is a partially or fully deacetylated form of chitin, a naturally occurring polysaccharide. Structurally, chitin is a polysaccharide consisting of beta-(1→4)2-acetamido-2-deoxy-D-glucose units, some of which are deacetylated. The degree of deacetylation usually varies between 8 and 15 percent, but depends on the species from which the chitin is obtained, and the method used for isolation and purification.
Chitin is not one polymer with a fixed stoichiometry, but a class of polymers of N-acetylglucosamine with different crystal structures and degrees of deacetylation, and with fairly large variability from species to species. The polysaccharide obtained by more extensive deacetylation of chitin is chitosan.
Like chitin, chitosan is a generic term for a group of polymers of acetylglucosamine, but with a degree of deactylation of between 50 and 100 percent. Chitosan is the beta-(1-4)-polysaccharide of D-glucosamine, and is structurally similar to cellulose, except that the C-2 hydroxyl group in cellulose is substituted with a primary amine group in chitosan. The large number of free amine groups (pKa=6.3) makes chitosan a polymeric weak base. Both chitin and chitosan are insoluble in water, dilute aqueous bases, and most organic solvents. However, unlike chitin, chitosan is soluble in dilute aqueous acids, usually carboxylic acids, as the chitosonium salt. Solubility in dilute aqueous acid is therefore a simple way to distinguish chitin from chitosan.
Chitosan is unique in that it is a polysaccharide containing primary amine groups. Chitosan forms water-soluble salts with many organic and inorganic acids.
It is known to prepare chitosan derivatives by attaching various groups to one or more hydroxyl groups of the chitosan, as in various cellulose derivatives, and/or in attaching various groups to the primary amino group of chitosan.
U.S. Pat. Nos. 3,879,376 and 3,953,608 disclose chitosan derivatives formed by acylation of chitosan with a saturated or unsaturated organic diacid anhydride. The chitosan derivatives contain 5 to 30% acetylglucosamine, 5 to 40% glucosamine, and 30 to 90% of glucosamine units reacted with the diacid anhydride. The derivatives are prepared in an aqueous dispersion. They may be recovered by the addition of a solvent such as an alcohol to precipitate the derivative. The derivatives are useful in various cosmetic compositions.
U.S. Pat. No. 4,996,307 discloses the preparation of an acylated chitosan having a degree of acylation of 35 to 65% by dissolving a water-insoluble chitosan having a degree of deacetylation of at least 70% in an aqueous acid solution, diluting the solution with water or a water-soluble solvent and adding an acylation agent to the diluted solution. Preferred water miscible solvents are lower monohydric alcohols such as methanol, ethanol, isopropyl alcohol, butyl alcohol, etc., polyhydric alcohols such as glycerin, propylene glycol, etc. and ketones such as acetone. Disclosed acylation agents are anhydrides of monocarbocyclic acids having from 1 to 5 carbon atoms per acyl group and benzoic acid.
U.S. Pat. No. 5,061,792 discloses the preparation of chitosan salts by suspending the chitosan in about 5 to about 50 parts by weight of a C
1
to C
3
monohydric alcohol containing an amount of water sufficient to raise the dielectric constant of the alcohol to at least about 30 and not more than about 40, adding about 0.5 to about 4 equivalents for each equivalent of amino groups in the chitosan of an acid, maintaining the mixture until reaction between the chitosan and the acid is complete, and recovering and drying the chitosan salt. The concentrations of water in the alcohol solutions ranges as follows: methanol—0%-9.7% by weight; ethanol—4.4%-13.7% by weight; 1-propanol—5.8%-13.4% by weight; 2-propanol—6.7%-14.4% by weight.
U.S. Pat. No. 4,929,722 discloses the preparation of chitosan salts in a heterogenerous reaction between dissolved organic acids and chitosan dispersed in aqueous alcohols, inter alia, containing an amount of water in an amount up to about 65 wt. % of the total medium, preferably 30 to 45 wt. %, more preferably about 40 wt. %.
The following papers disclose the reaction of chitosan with various anhydrides: (1) “Formation and Characterization of a Physical Chitin Gel,” L. Vachoud et al., Carbohydrate Research 302 (1977), 169-177; (2) “Chitosan Film Acylation and Effects on Biodegradability,” Jin Xu et al., Macromolecules 1996, 29, 3436-3440; (3) “N-Acetylchitosan Gel: A Polyhydrate of Chitin,” Shigehero Hirans et al., Biopolymers 15 (1976), 1685-1691.
SUMMARY OF THE INVENTION
We have now determined that aqueous alkaline fluids useful in oil and gas well operations, such as drilling, fracturing, sand control, lost circulation control, completion, workover and the like can be formulated to contain chitosan, an anhydride modifier, and a hydroxyl and/or amino-containing Polar Additive. The chitosan and anhydride react to increase the viscosity of the fluid. The Polar Additive increases the low shear rate viscosity and enhances the thermal stability of the fluids.
Thus, it is an object of the invention to provide aqueous alkaline well drilling and servicing fluids containing chitosan, an anhydride modifier, and a Polar Additive.
It is another object of the invention to provide an organic diacid anhydride-modified chitosan containing a Polar Additive as subsequently disclosed hereinafter.
Another object of the invention is to provide a method of drilling a well comprising circulating in a wellbore during drilling an aqueous alkaline fluid containing chitosan, an anhydride modifier therefore, and a Polar Additive as subsequently disclosed hereinafter.
Still another object of the invention is to provide a method of preparing an organic diacid anhydride-modified chitosan containing a Polar Additive as subsequently disclosed hereinafter.
These and other objects of this invention will be apparent to one skilled in the art upon reading this specification and the appended claims.
While the invention is susceptible of various modifications and alternative forms, specific embodiments thereof will hereinafter be described in detail and shown by way of example. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the invention is to cover all modifications and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.
The compositions can comprise, consist essentially of, or consist of the stated materials. The method can comprise, consist essentially of, or consist of the stated steps with the stated materials.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS
House Roy F.
Smith Diane M.
House Roy F.
Tucker Philip
Venture Innovations, Inc.
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